1. Field of the Invention
The present invention relates to superconducting magnets.
2. Description of Related Art
Because of the recent discovery of high critical temperature superconducting materials (such as high temperature superconducting oxides and MgB2), superconducting magnets can now be operated at relatively high temperatures. For example, superconducting magnets formed of one or more MgB2 superconducting wires having a critical temperature of approximately 30 K (Kelvin, absolute temperature) can be operated at approximately 10 K. An increase in operating temperature leads to cost reduction.
On the other hand, the higher the temperature of a superconducting coil, the higher the specific heat. Therefore, when the temperature of the coil locally increases, the temperatures of the other regions of the coil are less easily elevated. In other words, when a quench (i.e., a loss of superconductivity or a transition to a non-superconducting state) occurs at a region of a superconducting wire, heat due to the quench and the quench itself can less easily propagate into the other regions of the coil. As a result, the temperature of the quench initiation region tends to continue to increase and exceed a maximum allowable level, thereby possibly burning out the coil. Thus, in order to prevent burnout of a superconducting coil caused by a quench, it is important to propagate the quench as fast as possible.
A technique for suppressing quench occurrence in a superconducting magnet is disclosed in JP-A Hei 11(1999)-135318 (hereinafter Hayashi et al). The superconducting magnet of the above disclosure includes: a superconducting coil wound around a bobbin and supported by flanges; one or more good thermal conductive resin inserted through the superconducting coil; a vacuum container for containing and heat insulating the superconducting coil; and a refrigerator that is thermally connected to the superconducting coil in order to cool the coil to a extremely low temperature.
When a quench occurs, a possible disadvantage of the above disclosure is as follows: The resin inserted through the superconducting coil may result in insufficient velocity of the quench propagation because of a limitation of the thermal conductivity of the resin. Thus, for superconducting coils operating at a relatively high temperature of 10 K or higher, the technique of the above disclosure may not prevent burnout of the coil caused by a quench.